Of course they are made for folding - the cards are designed to run at 100%, 24/7. I won't discuss what the store clerk told you - that's him (her) to think this, and you to believe (or not) that fact.

Again, folding puts a lot of strain on the card, and good airflow / fan speed bump is mandatory in order to fold. My 275s are folding 24/7, with a fan speed of 75%. Temps are ~ 85C on a 472.

For your RMA, deal directly with BFG. Their warehouse is in Kahnawake (southshore of MTL) - if the turn-around time is slow, it's because they don't have any in stock, which happened to you and me last time.